There are two components of this research program. In Part I the specific aim is to study behavioral and neurochemical characteristics of rhesus monkeys from infancy through adolescence. We will determine whether these profiles can help predict the response to maternal separation, and whether the behavioral neurochemical response to maternal separation will in turn help predict the subsequent response to peer separation. The data to be obtained include social behavior, 24 hour activity, CSF amine and metabolite measures, and urinary MHPG levels. In Part II we will test the effects of phenelzine, haloperidol, and diazepam on rhesus monkeys' response to peer separation. The results from this part of the research will be relevant to model validation and will give a more complete picture regarding a spectrum of drugs and how they effect separation response in rhesus monkeys. Separation induced depression in rhesus monkeys has been proposed as one kind of animal model for human depression. Both aspects of this research concern themselves with the further development and validation of these models.